01 - Preheat your oven to 400°F. Lightly grease a baking dish with cooking spray or a small amount of olive oil.
02 - Butterfly each chicken breast by slicing lengthwise through the thickest part, being careful not to cut all the way through. Open the breast like a book to create two even halves connected by the center.
03 - Season both sides of the butterflied chicken breasts evenly with 1/2 teaspoon salt and 1/2 teaspoon black pepper, rubbing the seasoning into the meat.
04 - In a medium bowl, combine ricotta cheese, chopped spinach, 1/3 cup grated parmesan, shredded mozzarella, minced garlic, nutmeg, 1/4 teaspoon salt, and 1/4 teaspoon black pepper. Mix until well incorporated and smooth.
05 - Divide the spinach ricotta mixture evenly among the chicken breasts, spreading it over one half of each butterflied breast. Fold the other side over to enclose the filling completely.
06 - Secure each chicken breast with toothpicks along the edges if needed to prevent filling from escaping. Place the stuffed breasts seam-side down in the prepared baking dish.
07 - Brush the tops of each chicken breast with 1 tablespoon olive oil. Sprinkle the remaining 1/4 cup grated parmesan cheese evenly over all pieces.
08 - Bake for 25–30 minutes, or until the chicken is cooked through and reaches an internal temperature of 165°F when tested with a meat thermometer. The tops should be golden brown and crispy.
09 - Remove from oven and let the chicken rest for 5 minutes before serving. Carefully remove toothpicks, slice crosswise to display the filling, and serve immediately.